The versatile 27-year-old wasn't included in the Black Cats 18-man squad for their 2-0 League Cup success over Morecambe, with manager O’Neill confirming after the game that the player has been given permission to talk to another club.

"A club has made an offer for him and we, as a club, have accepted that, and it gives Kieran the opportunity to find out for himself,” O’Neill told reporters.

"If it doesn't materialise and he comes back, I'll still be pleased, but it's a position we might have to go and have a look at.

"Jack [Colback] played very, very well there, but Kieran wanted to pursue this and have a look at this, finding we had accepted the offer, and I will see what comes of it."

The 27-year old is in the final year of his contract and O'Neill hinted that if his departure is confirmed then the club will have to look for replacements during the final days of the transfer window.

He added: "It is something, if Kieran does go, that we would have to look at,"